Tracheostomy, an ancient surgical procedure originally described in the first century BC [1], is one of the more commonly performed procedures in modern intensive care, and is predicted to become more common as demand for intensive care services increases [2, 3]. While the benefits of early tracheostomy for patients who require extended periods of mechanical ventilation, compared to prolonged translaryngeal intubation, have been recently debated [4–6], the optimal method of performing tracheostomies in critically ill patients remains unclear.

The traditional method of performing tracheostomies in critically ill patients requires transport from the intensive care unit (ICU) to the operating theatre (OT), where a surgical team performs an open or surgical tracheostomy (ST). This involves a full dissection of the pretracheal tissues and insertion of the tracheostomy tube into the trachea under direct vision [7]. Percutaneous dilatational tracheostomy (PDT) was first described in 1957 [8], and became increasingly popular after the release of a commercially available kit in 1985 [9]. This technique involves the use of blunt dilatation to open the pretracheal tissue for passage of the tracheostomy tube. Proponents of PDT suggest that the limited dissection results in less tissue damage, lowers the risk of bleeding and wound infection, and is able to be performed at the bedside in the ICU, which may overcome the risks associated with transport of critically ill patients to the OT [10].

The proportion of patients receiving PDT and ST varies greatly in different practice settings, with ST being performed exclusively in some ICUs, PDT being performed almost exclusively in others and others using a mixture of both techniques [11–14]. Three previous meta-analyses have attempted to resolve which method of performing tracheostomies is superior; however, results from these reviews are limited for several reasons. One included both randomized and non-randomized studies [15]. The other two meta-analyses included only four [16] and five [17] randomized trials, respectively, made no attempt to find unpublished studies, made no assessment of the possible impact of publication bias, nor explicitly assessed the validity of those trials included. Current guidelines would suggest that meta-analyses lacking these features may arrive at unreliable conclusions [18]. As such, the question of whether PDT or ST is superior for critically ill patients remains unanswered.

To address these shortcomings and provide a comprehensive and contemporary overview, we performed a systematic review and meta-analysis to investigate whether, for adult critically ill patients who require an elective tracheostomy, PDT is superior to ST with regards to the incidence of wound infection, bleeding, and overall mortality as well as major peri-operative complications. We also examined whether one technique was associated with improved rates of longer-term complications.

This systematic review and meta-analysis has demonstrated that the technique of PDT has a number of important advantages over performing a ST in critically ill patients who require an elective tracheostomy. First, PDT was associated with a reduction in the incidence of clinically important wound infections compared with traditional ST. Secondly, and importantly, there was no evidence overall that PDT resulted in an increased incidence of clinically significant bleeding, major peri-procedural or long term complications. Finally, results of subgroup analysis suggested that PDT was superior to ST when the latter was performed in the OT; specifically, PDT was associated with a reduction in bleeding and overall mortality and a suggestion of decreased duration of translaryngeal intubation prior to tracheostomy.

It is not surprising that a reduced incidence of wound infection was found with the PDT technique. One of the reasons that minimally invasive surgical techniques have become more pervasive in many areas of surgery is the reduction in the rates of surgical site infections [41]. This may be due to minimization of the local tissue damage with a dilatational technique, or may in part be due to a relative preservation of immune functions when minimally invasive techniques are used when compared to an open technique [42].

While there was no statistically significant reduction in mortality with either technique, a possible trend towards lower mortality with use of PDT warrants further discussion. One plausible explanation for this observation could relate to the reduced incidence of infection in those receiving PDT. One study reported the death of a patient who had a ST that could be directly attributable to a local wound infection [28]. The ability to perform the PDT in the ICU without exposing patients to the risks of transport could contribute as well [43, 44]. This contention would be supported by the reduction in mortality with PDT when compared to ST performed in the OT. However, this finding is inconclusive and before a change in clinical practice could be recommended, this would need confirmation in a larger, adequately powered multi-center randomized clinical trial.

While subgroup analyses require cautious interpretation in general, the subgroup analysis in this systematic review provides some supportive evidence for the advantages of PDT over ST, in particular when the STs were performed in the OT. One considerable advantage of PDT is the relative safety and convenience of performing the procedure at the bedside in the ICU, which obviates the need to transport a critically ill patient. The transport of critically ill patients is often logistically difficult and exposes the patient to increased likelihood for adverse events and risk to safety [43–46]. The results of our analysis would support the assertion that the elective transport of critically ill patients to the OT for ST may pose undue and increased risk of complications and death.

Additionally, the suggestion of a reduction in the duration of translaryngeal intubation prior to the procedure when comparing PDT with ST performed in the OT may have several important clinical implications. This shorter waiting period prior to performing the PDT may be due to the ease of organizing the PDT at the bedside, specifically forgoing the need for a surgical consultation and the scheduling of time in often busy OTs. Only two studies [28, 39] have examined the time taken from the decision to perform a tracheostomy to the procedure being performed. Both found a significantly shorter time when the tracheostomies were performed using the PDT method. This may have additional implications for critically ill patients, including decreased duration of sedation, earlier weaning from mechanical ventilation and shorter overall length of stay in ICU [4, 47–49].

While long-term complications appear uncommon, the incomplete follow-up and lack of consistent definitions of outcome measurements in the available RCTs make conclusions difficult to draw with certainty. Non-randomized studies that have examined this issue have found that clinically relevant tracheal stenosis was uncommon in PDT when performed by experienced operators in a long-term study of 326 patients [50]. This experience is not universal [51, 52], and further investigation to determine how the method and timing of tracheostomy affects long-term outcomes is warranted.

Several clinical trials have compared the various methods of performing PDT, without any method being shown to be conclusively superior [53–56]. As the majority of studies included in this review used the multiple dilator technique, it is not surprising the results failed to demonstrate any particular benefit from one specific technique of PDT. While it has been suggested that the use of a bronchoscope to guide the operators performing the PDT makes the procedure safer [57], this was not supported by results of our analysis.

There are a number of potential limitations of our review that warrant discussion. Firstly, when considering the above findings, it is important to remember that several groups of patients were excluded from these RCTs, therefore limiting the generalizability of the results of this meta-analysis to all adult critically ill populations. Critically ill patients requiring emergency tracheostomy or with evidence or suspicion of difficult anatomy, prior airway problems, coagulopathies and previous tracheostomy were generally excluded. Thus, ST may still be indicated for selected patients, despite the continuing broader indications for use of PDT [58]. Secondly, while the role of the experience of the operators performing the procedures was presented in Table 1, the effect that the experience of the operators had on the outcomes could not be formally quantitatively assessed in this analysis. Thirdly, there was considerable heterogeneity in the definitions used across studies for the primary outcomes, in particular wound infection and bleeding. We have attempted to compensate for this by only reporting those episodes of wound infection, bleeding or other complications with obvious clinical relevance, requiring an intervention or that resulted in an alteration to patient management. Fourthly, the validity of our conclusions is, in part, dependent upon the validity of the primary RCTs included. Clearly, the practice of blinding is difficult to perform in surgical trials and it may not be possible to completely blind the adjudication of short-term outcomes. One method to partly address this problem is by setting a priori definitions for primary outcomes, as was done in some of the RCTs included in this review. In contrast, study design to maintain allocation concealment was conducted or reported in less than half of the reviewed RCTs. Interestingly, however, those RCTs that reported allocation concealment produced results similar to the overall pooled effect estimates. This may suggest that the conclusions of this meta-analysis are relatively robust to the influence of selected study quality factors. Finally, while there was no evidence of potential bias by inspection of the funnel plots, making significant publication bias unlikely, it is possible that studies were not identified for this review that could have had an impact on the pooled effect estimates.

Several important questions remain to be addressed regarding the use of tracheostomies in critically ill patients. While there is divided opinion as to the optimal timing of tracheostomy, there is as yet little definitive evidence to guide clinicians [4]. Similarly, there is a paucity of definitive evidence demonstrating that one technique of PDT is clearly superior to any other. Finally, the feasibility of determining whether any technique of performing a tracheostomy in critically ill patients is superior with regards to long term outcomes must be questionable given the difficulties in obtaining a large enough cohort and adequate follow up to address this issue.

We have demonstrated that use of PDT is associated with a reduced incidence of wound infection compared to ST in critically ill patients. PDT may yield an overall decreased risk of death when compared with ST. While PDT appears equivalent to ST for the overall incidence of clinically relevant bleeding, major peri-procedural and long term complications, subgroup analysis has revealed that PDT was superior to ST when the ST was performed in the OT. These results indicate that PDT, performed electively in the ICU, should be the method of choice for performing tracheostomies in critically ill adult patients.